pre_graph2:
cmp al,1 ; < 1 only if programmer error
jl gml0
; al >= 1
cmp al,8 ; VGA modes?
jg sgml1
; 1 <= al <= 8
mov si,ax ; э [1 .. 8]
dec si ; э [0 .. 7]
shl si,4 ; si *= 16 => [0=0, 1=16, 2=32, ..., 7 = 112] -- offset from table
add si,gr_table ; table row address table(gr_table) + nrow(al) * rowsize(16)
mov bx,[si+0] ; bx = col[0]
mov cx,[si+4] ; cx = col[2]
mov dx,[si+8] ; dx = col[4]